This invention relates generally to the use of nuclear energy to power a laser, and is particularly directed to solid state laser media driven by remote nuclear-powered fluorescence sources.
Lasers driven directly by nuclear energy are referred to as Nuclear Pumped Lasers (NPL). The concept of an NPL is not new, however, only about 30 different NPLs have been identified. In contrast, there are several thousand lasers driven by electrical discharges. A nuclear pumped laser uses the reaction products from nuclear reactions to electronically excite a laser media. The direct use of nuclear energy to power a laser has been a topic of interest for many years. Since nuclear power scales very well, a laser driven by the direct use of nuclear energy has the potential to scale very well. The nuclear reactions most frequently employed in NPL experiments are: 1) He.sup.3 (n,p)T {0.76 MeV energy release)}; 2) B.sup.10 (n,.alpha.)Li.sup.7 {2.35 MeV energy release}; and 3) U.sup.235 (n,vn)ff {200 MeV energy release}. There are other reactions which can be used as well, including Pu.sup.239 (n,vn)ff {200 MeV energy release}.
Early NPLs used the gamma ray yield of a thermonuclear explosion as their sole energy source. A successful laser driven by neutrons from a nuclear reactor is disclosed in U.S. Pat. No. 3,952,263, Fission Fragment Excited Laser System, to McArthur et al.
It is well known to laser physicists that high power densities are necessary to drive most lasers because the lifetime of the upper laser state is usually short (about 1 ms). However, the means of interfacing the nuclear fuel to the laser media in conventionally driven NPLs leads to inherently low power densities (less than 10 Kw/cm.sup.3). These low power densities in return are the limiting factor on the number of NPLs which can be discovered. On the other hand, electrically driven lasers can achieve power densities greater than 100 Kw/cm.sup.3.
The limitations of conventionally driven NPLs can be overcome. Two new methods of interfacing the nuclear fuel to the laser have been developed which should allow many more NPLs to operate.
The first method, the transfer method, allows the nuclear energy to be transferred to an intermediate atomic or molecular species with a long lifetime. This intermediate species can be transported away from the nuclear energy source and mixed with a second medium. If the second medium is chosen correctly, then the energy from the intermediate atomic or molecular species can be collisionally transferred to generate the upper energy level. An example of the transfer method was achieved using N.sub.2 (.nu.=1) as the intermediate energy carrier and CO.sub.2 as the laser medium.
The second method, the photolytic transfer method, allows the nuclear energy to be converted to fluorescence through the interaction of the reaction products with a surrounding medium. The basic idea of the photolytic transfer method evolved from unsuccessful attempts to directly drive the XeF(B-X) laser. An early experiment using the photolytic transfer method used an Argon excimer fluorescence source excited by the B.sup.10 (n,.alpha.)Li.sup.7 reaction and a N.sub.2 O laser media to generate the O(.sup.1 S) group VI laser. It was subsequently discovered that the XeF(B-X) laser produced copious amounts of narrow band fluorescence, but that the upper laser level lifetime was so short (about 17 ns), that the power density required to drive the laser was too high to achieve with conventional nuclear-pumping methods. Hence, the narrow band fluorescence efficiency was measured and found to be 11.+-.5%. It was concluded that XeF(B-X) and excimers in general would be excellent fluorescers for photolytically driven laser experiments.
In an earlier development by the applicant and others, diffuse light from a volume source was coupled to the reactant, and a process for reactions other than the production of a laser (e.g. photochemical or photoelectric reactions) was used. This development, termed a nuclear-pumped energy focus, was used to drive high energy/power laser systems. A nuclear-pumped energy focus was disclosed in an article by M. A. Prelas and G. L. Jones, entitled Design Studies of Volume-Pumped Photolytic Systems Using a Photon Transport Code, published in H. Appl. Physics, 53(1), 165 (1982); in an article by M. A. Prelas and S. K. Loyalka, entitled A Review of the Utilization of Energetic Ions for the Production of Excited Atomic and Molecular States and Chemical Synthesis, published in Progress in Nuclear Energy, 8, 35-52 (1981); and in an article by M. A. Prelas et al., entitled Nuclear-Pumped Laser Research at the University of Missouri, published in Trans. Am. Nucl. Soc., 34, 810 (1980).
The present invention is an improvement in the concept of a photolytic transfer, nuclear-pumped laser. The invention utilizes an improved nuclear fluorescence source to drive a solid state laser remote from the nuclear fuel.
Accordingly, it is an object of the present invention to provide a solid state laser capable of being driven by remote nuclear powered fluorescence sources.
Another object of the present invention is the use of radiation hardened waveguides to channel the optical power emitted from the fluorescence source near the nuclear fuel to a remote radiation sensitive solid state laser.
It is another object of the present invention to use solid state lasers which have the lowest driver power requirements of any photolytically driven laser.
Yet another object of the present invention is the use of improved nuclear fluorescence sources.